Nancy Pelosi and other "pro-choice Catholics" (a contradiction of terms) have publicly stated that many of the early Church Fathers held a lax position on abortion and that the Church's thoroughgoing condemnation of abortion is not "historic."
Typically "pro-choice Catholics" appeal to statements in the writings of the Church Fathers that may indicate a faulty understanding of "fetal ensoulment," that is to say, the moment at which a human soul becomes present with respect to the moment of conception.
Don't be fooled by these arguments. It is true that many thinkers were confused about gestation prior to modern medicine (and sonograms). Nevertheless, the Church Fathers were unanimous in their condemnation of abortion.